1. Field of the Invention
The present invention relates to stereolithographic apparatus and method for preparing a mask having a mask pattern, exposing a hardenable resin or the like through the mask pattern to hardening-promoting medium such as light, heat, pressure, electromagnetic waves or the like in the form of a plane to harden the hardenable resin or the like, thereby forming a three-dimensional object.
2. Description of the Related Art
A stereolithographic system using a photolithographic apparatus for optically manufacturing a three-dimensional object (hereinafter the process of forming a three-dimensional object by using stereolithography will be referred to as “stereolithographic molding”) have been known in the art. The photolithographic apparatus generally includes a controller based on a three-dimensional computer-aided design (3D-CAD) for outputting stereolithographic data.
In the photolithographic apparatus, photohardenable resin is scanned and exposed by a laser beam from a semiconductor laser or the like in accordance with the above data from the controller to photoharden the photohadenable resin. In this case, however, the system has a disadvantage that it needs much time to expose each resin layer to light in order to harden the resin layer.
In recent years, another type of photolithographic system has been proposed to overcome the above disadvantage. The system performs the process comprising the steps of preparing a mask for high-speed stereolithography, and exposing the surface of each layer of hardenable resin (that is, an unhardened resin layer) to ultraviolet (UV) rays from an UV lamp in the form of a plane through the mask at a time (this exposure process will be hereinafter referred to as “plane exposure”).
In order to perform the above exposure process, a mask pattern is formed on a light-transmissible member by using electrostatic toner to form a mask, the mask thus formed is superposed on a hardenable resin layer, and then UV rays are irradiated through the mask to the hardenable resin layer to thereby expose the hardenable resin to the UV rays in the form of a plane.
In the construction of the conventional system as described above, warp can be generated in the photohardenable resin as a result of shrinkage on hardening when the plane exposure is conducted on photohardenable resin (i.e., the photohardenable resin is exposed to UV rays in the form of a plane at a time). In this case, therefore, there is a trouble in which the stereolithographic molding accuracy is lowered more remarkably in comparison with so-called linear exposure using a laser beam.
Furthermore, in the above construction, since UV rays must irradiated through the mask to the unhardened resin layer while the mask is superposed on the unhardened resin layer, the edges of the finally hardened resin portion may be blurred (spread) due to the diffraction effect of light by the mask pattern, and thus the UV rays must be collimated to prevent the diffraction effect of the mask pattern.
In order to collimate the UV rays, the use of grid has been proposed. However, the amount of light might be reduced by about 10% if the grid is used, so that there is another problem that the hardening time will be increased by almost 10 times.
Alternatively, if the output power of the optical source is increased, the hardening time could be shortened. In this case however, working electric power will be increased, resulting in the increase in a running cost of the system.
In general, the light source may be selected from a mercury lamp, a metal halide lamp, an UV fluorescent lamp or the like. If such a light source is used, it stays on during the exposure. Thus, the exposure and interception of the light emitted from the light source to an exposure target must be controlled by using a shutter.
Any light source listed above has a large calorific value, so that an ambient temperature of the system can be extensively increased. Therefore, it is necessary to install some cooling device to prevent the system from overheating. In particular, otherwise, the shutter deforms with the heat of the light source, resulting in occurrence of some trouble such as a malfunction or the like.